1. Field of the Invention
This invention relates to an apparatus for detecting the in-cylinder pressure of an internal combustion engine having a plurality of cylinders and for providing pressure parameters.
2. Prior Art
There has hitherto been commonly known an apparatus for detecting the pressure of cylinders of a multi-cylinder engine to analyze the characteristics thereof, as shown in FIG. 1 and which comprises an engine 1 having #1-#4 cylinders 2-5, pressure sensors 6-9 for detecting the pressures in the respective cylinders 2-5, a crank angle sensor 10 for generating pulses in response to the crank angle of the engine 1 to determine the timing of the pressure detection and an in-cylinder pressure measuring section 11 for receiving outputs from the pressure sensors 6-9 and the crank angle sensor 10 to measure the pressures in the cylinders. The pressure measuring section 11 includes interfaces (I/F) 12-15 for converting the outputs from the pressure sensors 6-9 to voltage values, a timing interface 16 which receives the output of the crank angle sensor 10, A/D converters 17-20 for converting the outputs from the interfaces 12-15 to digital values, memories 21-24 for storing the digital values from the A/D converters 17-20 and a data collecting/analyzing device 25 which receives the outputs of the timing interface 16 and memories 21-24, generates outputs to the A/D converters 17-20 and memories 21-24 to control the number of data samples and the commencement and termination of measurement, and performs the analysis of the measured data. The data collecting/analyzing device 25 may be constituted by a personal computer, for example, and the pressure measuring section 11 is commercially available.
With the above-described arrangement, the pressure sensors 6-9 detect the pressure in the cylinders 2-5 and the crank angle sensor 10 generates a basic angle pulse for each predetermined interval (interval of 1.degree. of the crank angle, for example). The outputs from the pressure sensors 6-9 are input through the interfaces 12-15 and the A/D converters 17-20 to the memories 21-24 and stored therein as the digital values and further are input to the data collecting/analyzing device 25. The output from the crank angle sensor 10 is input through the interface 16 to the data collecting/analyzing device 25. According to these inputs, the data collecting/analyzing device 25 continuously collects data at predetermined crank angle intervals, the number of samples being determined by the capacity of the memories 21-24, analyzes the data after the termination of collection and provides evaluation indices indicating the engine characteristics, such as changes in pressure in P(.theta.) (correlation between the pressure and crank angle) diagram, P-V (correlation between the stroke volume and pressure) diagram, Pi (indicated mean effective pressure), etc.
In the above-described prior apparatus, however, it is essentially impossible to make a real-time measurement, because the prior apparatus is of a type in which the pressure data are continuously collected and stored and then arranged to provide the evaluation indices for analyzing the characteristics. Thus, the prior apparatus is not suitable, for example, for an engine control arranged so that the engine operation characteristics are detected and corrected or modified when they are deteriorating. There are further problems such that in order to evaluate the engine performance it is necessary to provide a certain number of combustion cycles for data collection, for example, at least 30 cycles is necessary for an acceleration test from an idling condition of 750 rpm to 6000 rpm, and this requires that the memories 21-24 have a capacity of 21.6 Kbytes [=30 (cycles).times.720 (one stroke crank angle of 4-cycle engine).times.1 byte (capacity for storing the ordinary amount of pressure data)]. If 2 bytes is necessary to store the pressure data, the capacity must be doubled and the cost will increase accordingly.